Discharge lamp with HO radicals as radiating additives

ABSTRACT

The method of producing optical radiation and a discharge lamp for that purpose pertain to electrical technology, specifically to methods of producing radiation in the visible spectrum resulting from electrical discharge in gas, and to low-pressure discharge lighting lamps of various types. The proposed method of producing optical radiation, and the associated discharge lamp, extend the available range of environmentally clean lighting systems. The method involves creating a gas discharge in an inert gas atmosphere with a radiating additive in an optically transparent tube. A novelty of the method lies in the use as a radiating additive of the HO radical. The discharge lamp comprises an optically transparent tube (1) filled with an inert gas and a radiating additive. Also novel is the use as a radiating additive of an HO source obtainable from water or group II metal alkalis.

TECHNICAL FIELD

The present group of inventions relates to the electrical engineeringindustry, more specifically to methods of generating radiation in thevisible spectrum as a result of an electrical discharge in gas, and alsoto low-pressure discharge illumination lamps of various types: argon,xenon, krypton, sodium, mercury, mercury-luminescent et alia.

KNOWN ART

A method is known of producing optical radiation, comprising thecreating of a gas discharge in a mixture of sodium vapours at a pressureof 0.1-1.0 Pa with inert gases at a pressure of 100-1500 Pa in a tube ofoptically transparent material (cf. G. N. Rokhlin "Discharge lightsources", Moscow, Energoatomizdat, 1991, pp. 451-457).

Said known method of producing optical radiation is based on thefluorescent radiation of sodium vapours (589.0 and 589.6 nm), i.e.almost monochromatic yellow light that cannot be transformed by means ofphosphors, as a result of which said method is unsuitable for generallighting. In order to accomplish said method, the use of a chemicallyaggressive substance--sodium--is required.

A gas discharge lamp is known comprising a glass tube into which twoelectrodes are hermetically sealed. Said tube is filled with neon plus0.5-1.0% argon at a pressure of up to 600 Pa, said sodium is likewiseintroduced into the tube. The tube is externally provided with smallconvexities (internal dimples) for condensation of the sodium and isfitted inside an evacuated outer glass envelope whose inner surface iscoated with a thin indium oxide film (cf. G. N. Rokhlin "Discharge lightsources", Moscow, Energoatomizdat, 1991, pp. 451-457).

The known discharge lamp allows only a monochromatic yellow light to beobtained that cannot be transformed by means of phosphors, and moreovercontains sodium, a chemically aggressive substance.

A method is known of producing optical radiation, comprising thecreating in a tube of optically transparent material of a gas dischargeof varying lengthwise cross-section in an inert gas and mercury vapouratmosphere. The magnitude of the current and pressure in the dischargespace is selected so as to ensure the periodic interruption of discharge(see RF patent specification No. 1814741, c1. H01J 61/72, pub.07.05.93).

Said known method allows radiation to be generated in the UV, visibleand near-IR regions of the spectrum with high efficiency and brilliance.However, the use of mercury vapour renders it environmentally hazardous.

A mercury gas discharge lamp is known for lighting cucumber greenhousescomprising an optically transparent discharge chamber with electrodessealed therein and filled with inert gas and mercury in such quantity asto maintain the operating pressure during discharge and with radiatingadditives in the form of lithium, sodium and indium iodides in thefollowing quantities (% wt.): lithium iodide 8-18; sodium iodide 70-88;indium iodide 4-12 (cf. RF patent specification No. 1816330 c1. H01J61/18, publ. 15.05.93).

The presence of mercury as a working substance is undesirable from theviewpoint of the environmental friendliness of the fabrication,operation and subsequent disposal of such lamps.

The method that is closest, in terms of the totality of substantivefeatures, to the claimed method is a prototype method of producingoptical radiation comprising the creating in a tube of opticallytransparent material of a gas discharge in an atmosphere of inert gas,mercury vapour and radiating additives in the form of metal halides atan inert gas pressure of 2660-39900 Pa (cf. USSR Inventor's CertificateNo. 1833927 c1. H01J 61/18, publ. 15.08.93).

The known method, by virtue of the introduction of radiating additivesof various metals, allows high-power lamps to be produced that embracethe most varied radiation spectrum at significantly higher efficienciesas compared with mercury-only lamps.

A drawback of said prototype method is that mercury has to be employedwhich is extremely undesirable from the viewpoint of environmentalfriendliness.

The lamp that is closest, in terms of the totality of substantivefeatures, to the claimed discharge lamp embodying the method is aprototype discharge lamp comprising an discharge chamber of opticallytransparent material with sealed-in electrodes and filled with inertgas, mercury and additives supplying halides of radiation metals to thedischarge chamber, for which purpose additives supplying silver, copperand zinc halides to the discharge chamber are used, said constitutentsbeing employed in the following quantities (μmol/cm³):

    ______________________________________                                               Mercury                                                                              1.5-45.0                                                        ______________________________________                                    

Additives supplying to the discharge chamber halides of:

    ______________________________________                                               Silver                                                                               0.5-12.0                                                               Copper                                                                              0.3-9.0                                                                 Zinc  0.2-8.0                                                          ______________________________________                                    

while the inert gas pressure measure 1.33-39.9 kPa (cf. RF patentspecification No. 17263 c1. H01J 61/18, pub. 30.07.94).

Notwithstanding all the advantages of the known prototype discharge lampit is not environmentally friendly on account of the presence of mercuryduring the fabrication, operation and subsequent disposal thereof.

DISCLOSURE OF INVENTIONS

The aim of the present group of inventions was to broaden the availablerange of means of producing optical radiation by creating anenvironmentally clean method of producing optical radiation and adischarge lamp for that purpose.

The stated aim is achieved by using, in the method of producing opticalradiation comprising the creating in a tube of optically transparentmaterial of a gas discharge in an atmosphere of inert gas with aradiating additive, the HO radical (hydroxyl group) as radiatingadditive. The hydroxyl radical HO may be formed by various means: byfeeding water vapour into the discharge or by heating group II metalalkalis situated in the tube wherein discharge is accomplished.

The stated aim is likewise achieved by introducing an HO radical source,in a discharge lamp embodying the method of producing optical radiationand comprising a tube of optically transparent material filled withinert gas and radiating additive, in order to form said radiatingadditive. For lighting purposes, the HO radical source if introduced ina quantity of 10⁻¹¹ -10⁻⁷ mol/cm³. As the cheapest and simpliest HOradical source, water of some substance containing the hydroxyl groupmay be used. Group II metal alkalis, e.g. Ca(OH)₂ or Mg(OH)₂, which whenheated disassociate into highly stable oxides and water, may beexpediently used as such a source.

The claimed group of inventions is based on the phenomenon surprisinglydiscovered by the inventors whereby the radiation spectrum of gasdischarge in an inert gas undergoes a qualitative change on introductionof the HO radical therein. Introduction of the hydroxy HO fundamentallychanges the properties of discharge, particularly its radiationcharacteristics. In the absence of the hydroxyl, the characteristics ofgas discharge are determined by the inert gas atoms and ions. Duringglow discharge, maximum radiation of the energized inert gas atomscoincides with fluorescent radiation in the vacuum UV region. Onintroduction of the HO radical, discharge radiation changes into theradiation of HO molecules alone to all intents and purposes, whosefluorescent radiation forms a 306.4 nm band lying in the near-UV regionof the spectrum. HO radical radiation may be used direct, e.g. intechnological processes or to irradiate vegetation and living organisms(as such radiation lies approximately in the middle of the 280-350 nm UVradiation region that has the most beneficial effect on vegetation andliving organisms including man), and may also be transformed veryefficiently, by means of the appropriate phosphor applied on the wall ofthe outer envelope enclosing the tube in which gas discharge isaccomplished (the so-called discharge chamber), into the visible regionof the spectrum. Hydroxyl molecules are readily obtained during glowdischarge, e.g. from water molecules. On interruption of discharge fromthe hydroxyl radicals, water molecules are formed anew. This makes theuse of hydroxyl absolutely harmless. The potentials required forionization and for energizing the HO radicals (12.9 V and 4.0 Vrespectively) are substantially lower than the corresponding potentialsfor the atoms of the inert gases argon, helium, neon and krypton, whichallows discharge conditions to be created in which the inert gas becomesa buffer gas, with a small addition of the HO radical acting as theactive element of gas discharge. The fluorescent nature of the radiationof the energized HO radical ensures that electrical energy istransformed into electromagnetic radiation energy in the UV region ofthe spectrum highly efficiently.

BRIEF DESCRIPTION OF DRAWINGS

The claimed method of producing optical radiation and the claimeddischarge lamp are illustrated in the drawings, wherein:

FIG. 1 shows the HO radical's radiation spectrum;

FIG. 2 shows the discharge lamp's radiation spectrum; a--lamp is filledwith argon (at a pressure of 3857 Pa and discharge current 30 mA);b--lamp is filled with argon (at a pressure of 3857 Pa and dischargecurrent 30 mA); with addition of the HO radical obtained duringdischarge from water;

FIG. 3 shows the discharge lamp's radiation spectrum; a--lamp is filledwith helium (at a pressure of 2660 Pa and discharge current 60 mA); b--alamp is filled with helium (at a pressure of 2660 Pa and dischargecurrent 60 mA) with addition of the HO radical obtained by dischargeheating of calcium hydroxide;

FIG. 4 shows a cross-section of the UV radiation discharge lamp;

FIG. 5 shows a cross-section of the discharge lamp with phosphor;

FIG. 6 shows a cross-section of an embodiment of the discharge lampwithout electrodes.

In FIGS. 1-3, the horizontal axis represents radiation wavelengths in nmand the vertical axis the radiation intensity in relative units.

As can be seen in FIGS. 26 and 34, introduction of the HO radical intothe discharge causes a fundamental change in the spectrum: the inert gaslines are virtually absent and all the radiation is found to beconcentrated in the hydroxyl's 306.4 nm band. The type of inert gas doesnot basically change the nature of the spectrum: analogous results wereobtained when neon and krypton were introduced into the lamp as insertgas.

As seen in FIG. 4, the discharge lamp comprises a hermetically sealedtube 1 (discharge chamber), made of optically transparent material e.g.quartz, ceramic or UV-transmitting glass with sealed-in electrodes 4, 5and appendages 8 for an HO radical source 7. In the embodiment with aphosphor coating (FIG. 5), the hermetically sealed tube 1 is situated inan external evacuated (to reduce heat exchange) envelope 2 on whoseinner surface a phosphor coating 3 has been applied in order totransform the spectrum of the radiation being generated from the UVregion to the visible region. The hermetically sealed tube 1 is filledwith inert gas (e.g. argon, helium, xenon, krypton or mixtures thereof).

The tube 1 may be furnished with operating electrodes 4 and 5 (e.g.tungsten electrodes), whereas in the alternative embodiment withoutelectrodes (FIG. 6) such electrodes are absent and in order to activatedischarge use is made of a high-frequency coil 6 connected to ahigh-frequency generator (not shown in diagram). The HO radical source7, e.g. Ca(OH)₂, may be situated behind the electrodes 4 and 5, in theappendages 8 of tube 1 (FIGS. 4 and 5); or outside the coil 6 (FIG. 6).

EMBODIMENTS OF THE INVENTIONS

The claimed method is accomplished with the aid of the discharge lamp inthe following manner. As HO radical source, water is placed in the lamp.The voltage required to activate discharge in tube 1 is applied toelectrodes 4 and 5 (to coil 6 in the non-electrode embodiment of thelamp). Between electrodes 4 and 5 an electrical discharge is producedwhile envelope 1 is heated. Water vapour enters the electrical dischargezone to form HO radicals. Optical radiation in the UV region is therebyproduced. If optical radiation of some other spectral composition isrequired, an appropriate phosphor coating 3 is applied to the innersurface of envelope 2 to transform the UV radiation from tube 1 into thevisible region of the spectrum.

EXAMPLE 1

A discharge lamp was fabricated in the form of a quartz cylindricaltube, 20 mm in diameter, at the extremities of which two tungstenelectrodes were sealed in. In the middle of the tube an appendage wasmade in which calcium alkali was placed. The tube was connected up to avacuum system. Tungsten coils were wound onto the tube and appendage toheat the discharge chamber, with the tube wall temperature and appendagetemperature being varied independently of one another. The temperaturewas measured by means of thermocouples situated on the tube wall and thesurface of the appendage. The tube was first evacuated by means of thevacuum system and then filled with argon up to a pressure of 3857 Pa. Adirect-current voltage of 600 V was applied to the electrodes sufficientto spark over the distance between the electrodes, whereupon the voltagewas reduced to 300 V. The radiation emitted by the axial dischargeregion was focused on the inlet aperture of a spectrum instrument whoseoutlet was connected via a photoelectron multiplier and amplifier to arecording instrument to record the discharge radiation spectrum in the200-800 nm wavelength range. The radiation spectrum recorded by theinstrument is shown in FIG. 2(a). It represents the radiation of theargon atoms filling the lamp tube. Then the HO radical source (Ca(OH)₂)in the lamp's appendage was heated until it disassociated into water andcalcium oxide. The water vapour entering the discharge region formed HOradicals. The discharge lamp's optical radiation in the presence of HOradicals was recorded and the radiation spectrum is shown in FIG. 2(b).The argon lines were "suppressed" and a new line appeared in the UVregion of the spectrum (306.4 nm).

EXAMPLE 2

A non-electrode discharge lamp was fabricated from a quartz tube, 10 mmin diameter, which was connected up to a vacuum system. A high-frequencycircuit was wound onto part of the tube's surface and the central partof the tube was provided with an appendage in which water was placed.Tungsten heating coils were wound onto the tube walls and the appendageto allow the tube wall temperature and appendage temperature to bevaried independently of one another. The discharge lamp was firstevacuated (without water in the lamp's appendage) by means of the vacuumsystem and then filled with argon up to a pressure of 3857 Pa. Dischargein the lamp was activated by means of a high-frequency electromagneticfield with a frequency of 100 MHz. The radiation spectrum was recordedin the same way as in example 1. After the radiation of the argon in thelamp's appendage had been recorded, water was introduced and heated bymeans of the tungsten coil. The recorded spectra coincided with thespectra obtained in example 1.

EXAMPLE 3

A non-electrode discharge lamp fabricated as in example 2 was filledwith helium up to a pressure of 2660 Pa. The discharge lamp's radiationspectrum was recorded in the absence of HO radicals (FIG. 3(a)). Theradiation spectrum represented the radiation of the helium atoms. Thenmagnesium alkali was placed in the lamp, discharge was activated and thelamp's radiation spectrum was recorded (cf. FIG. 3(b)). Comparison ofthe spectra in FIGS. 3(a) and 3(b) shows that radiation in the HOradical's band (306.4 nm) predominates.

EXAMPLE 4

A non-electrode lamp fabricated as in example 2 was filled with neon ata pressure of 288 Pa. The radiation spectra were recorded in the absenceof HO radicals and after water had been added into the lamp. With HOradicals present in the discharge, the neon lines were virtually absentand all the radiation was found to be concentrated in the hydroxyl's306.4 nm band.

Commercial applicability

The inventive method of producing optical radiation and the dischargelamp for that purpose may fine a use in industry and agriculture, intransport and for the lighting of populated areas andresidences--everywhere where low-pressure discharge lamps of varioustypes are currently used for lighting purposes.

What is claimed is:
 1. Discharge lamp comprising a tube (1) of opticallytransparent material filled with an atmosphere consisting essentially ofinert gas and radiating additive consisting of HO radicals, wherein anHO radical source is introduced to form the radiating additive, andfurther comprising means for maintaining a discharge in the atmosphere.2. Discharge lamp as claimed in claim 1, characterized in that the HOradical source is introduced in a quantity of 10⁻¹¹ -10⁻⁷ mol/cm³. 3.Discharge lamp as claimed in claim 1, characterized in that as HOradical source, water is used.
 4. Discharge lamp as claimed in claim 1,characterized in that as HO radical source, a substance containing thehydroxyl group is used.
 5. Discharge lamp as claimed in claim 4,characterized in that as substance containing the hydroxyl group, agroup II metal hydroxide is used.
 6. Discharge lamp as claimed in claim5, characterized in that as group II metal hydroxide, magnesium orcalcium hydroxide is used.